The present invention relates to the catalytic cracking of hydrocarbons, for example petroleum fractions. In another aspect, this invention relates to a method for countering the adverse effects that contaminating metals have on crystalline zeolite aluminosilicate cracking catalysts.
It is well known to employ catalysts for cracking, i.e. the conversion of relatively high molecular weight hydrocarbons, such as gas oil, petroleum residuum, and the like, to relatively low molecular weight hydrocarbons such as naphtha. As in any catalytic process deactivation of the catalyst is a significant economic factor in cracking.
Factors contributing to the deactivation of cracking catalysts include coke formation and the formation of deposits of contaminating metals such as nickel, vanadium, iron, and copper. These metals can come from erosion of the metallic equipment or from corresponding metals and metal compounds in the hydrocarbon feed. The coke can generally be removed by exposing deactivated catalyst to regeneration wherein the carbonaceous materials thereon are consumed by combustion.
U.S. Pat. No. 2,575,258 discloses countering the adverse effects of contaminating metals on certain cracking catalysts by exposing the catalyst to combustive regeneration followed by reduction with a reducing gas such as hydrogen. That patent does not, however, indicate whether such a process would be effective on zeolitic cracking catalysts of the type currently used in most modern cracking operations.
It is well recognized that zeolite and amorphous cracking catalysts are affected differently by contaminant metals. In amorphous cracking catalysts, these contaminant metals are deactivated by successive cracking cycles as a greater rate than on zeolitic cracking catalysts (Cimbalo, et al, Oil and Gas Journal, May 5, 1972, p. 112). Although a given level of contaminant metals has a greater effect on amorphous catalysts than on zeolitic catalysts, the long term effect is such that contaminant metals become significant in their effect on zeolitic cracking catalysts.
An object of the present invention is to provide a process for countering the adverse effect of contaminating metals on a crystalline zeolite cracking catalyst.
Other aspects, objects, and advantages of the present invention will be apparent from the following description.
In accordance with the present invention, there is provided a process for improving the activity of a cracking catalyst comprising crystalline zeolite aluminosilicate containing contaminating metals, said process comprising contacting said cracking catalyst with a reducing gas under suitable conditions. Where the cracking catalyst is a used catalyst having carbon deposited thereon, it is preferred to subject the catalyst to regeneration with a combustion supporting gas prior to contacting the catalyst with the reducing gas. The present invention is particularly beneficial for use with zeolite cracking catalysts containing antimony. In another aspect, the present invention relates to a process for catalytic cracking in which the zeolite cracking catalysts is improved by contact with a reducing gas.
Conditions necessary for catalytic cracking with crystalline zeolite aluminosilicate catalysts are well known in the art. The crystalline zeolite aluminosilicate cracking catalysts are generally comprised of a minor but catalytically active amount of the zeolite dispersed in an amorphous cracking catalyst. Typically, the cracking is conducted at temperatures in the range of about 800xc2x0 F. to about 1200xc2x0 F. Pressures can generally range from subatmospheric to about 3000 psig. Typically, the weight ratio of catalyst to hydrocarbon feed is in the range of about 3.1 to 30:1.
The hydrocarbon feed can include any that can be cracked to lighter products. Typical feeds include gas oils, fuel oils, cycle oils, slurry oils, topped crudes, oil from tar sands, heavy residual and the like. Many of the feeds currently employed contain at least one of the metals nickel, vanadium, and iron, generally in amounts within the ranges set forth in the following table:
In regeneration carbonaceous materials on the used cracking catalyst are removed by contacting with a combustion-supporting gas, such as air, at a temperature sufficient to result in combustion of accumulated carbon. Typically, the regeneration is conducted at temperatures in the range of about 950xc2x0 F. to 1500xc2x0 F.
In the reducing step the registered catalysts is contacted with a reducing gas. Generally any suitable reducing gas can be employed. Examples include carbon monoxide, hydrogen, propane, methane, ethane, and mixtures thereof. Accordingly sources of reducing gas can include regenerator off gases or light gaseous streams from the cracker. It is currently preferred to employ a reducing gas containing hydrogen. The volume of reducing gas employed in contacting the catalyst and the temperatures and pressures maintained should be adjusted so as to convert substantially the contaminating metal oxides present in the catalyst to compounds having substantially less or no detrimental effect on the activity of the catalyst. Depending upon the nature of the contaminating materials and upon the amount and kind of reducing atmosphere employed, the temperature at which the contaminated catalyst is contacted with the reducing atmosphere can vary, but generally will be reduced within the range of 850xc2x0 F. to about 1300xc2x0 F. Inasmuch as the pressure maintained in the several known catalyst cracking processes may differ and since the pressure maintained will have an influence on the reactions which take place in the reducing atmosphere, the temperature and throughput must be correlated in each instance with the pressure maintained in the particular unit. It should be remembered that the volume of reducing gas required will also depend upon the nature and amount of the contaminating oxides. When relatively small quantities of contaminating oxides are present in the catalyst, very small volumes of reducing gas and/or short contact times may be employed with satisfactory results, while when relatively large quantities of contaminating oxides are present in the catalyst larger volumes of reducing gas and/or long contact times will be required. Typically the amount of hydrogen injected will be in the range of about 0.1 to about 20 standard cubic feet per minute per pound of contaminating metals on the catalyst. Contact times will generally be in the range of about 0.05 minutes to 2 hours, preferably about 5 to about 30 minutes.
The present invention can be used in conjunction with other techniques for countering the adverse effects of contaminating metals. Thus the reduction can be applied to crystalline zeolite cracking catalysts that have been treated with agents known to counter the adverse effect of such contaminants. A number of such agents are known in the art. Typical are those disclosed in U.S. Pat. No. 2,901,419; 3,711,422; 4,025,458; and 4,031,002, the disclosures of which are incorporated herein by reference. The reduction technique is particularly beneficial when employed on a crystalline aluminosilicate zeolite cracking catalyst which contains passivating amounts of antimony.
As is known in the art, the amount of antimony needed to achieve a given level of passivation can vary depending upon the level of metal contaminants. Typically the antimony is employed in an amount such that the catalyst will contain antimony in an amount in the range of about 0.005 to about 10 weight percent, preferably about 0.01 to about 2 weight percent. The antimony can be added to the catalyst in any suitable manner. A currently preferred manner involves including suitable amounts of an antimony compound in the hydrocarbon feed.
A further understanding of the present invention will be provided by the following examples.